1. Technical Field
The invention relates to a method for manufacturing filler elements from expanded material, as well as a device for implementing such method.
2. Background Art
Expanded material can be produced from any thin foil, usually made of metal, paper, wood, but also plastic, in which a large number of individual cuts are initially made, all running parallel to but offset in relation to each other; next the material is stretched transversely to the orientation of these cuts, thus producing a more or less two-dimensional lattice structure comprising, for example, rhomboidal openings and interlying webs of foil whose thickness corresponds to the spacing between the cuts.
Depending on the choice of material and also the selected thickness of the material, an expanded metal of this kind can be put to a wide number of uses: starting with very thin lattices, which can be used to Provide explosion protection in tanks, fire protection in general, and similar applications, the uses can range all the way up to the production of stair treads, catwalks, and the like, when sheet metal several mm thick is used.
One of the applications for expanded material, which is referred to hereafter exclusively as expanded metal, also consists of manufacturing filler elements of a certain size and shape by appropriately working the substantially two-dimensional lattice structure. These filler elements are then placed inside tanks containing explosive liquids. If such a container is ignited, the explosive gas accumulated in the free space of the container does not explode, but instead the contents of the container burn in a normal and controlled manner. Although to achieve this protection the containers must be completely filled with the filler elements, these filler elements possess such a large percentage of cavities that the holding capacity of the container for liquid materials is reduced by no more than about 1 percent to 6 percent when it is filled with filler elements.
In order to achieve this, it is obvious that the filler elements, in addition to being identical in size and shape, should also possess approximately the same density and thus foil massy because the explosion-preventing affect can only be reliably achieved, while simultaneously limiting the reduction in the container volume, if the metal foil is uniformly distributed within the filler elements and if, in turn, the filler elements are uniformly distributed in the container--this latter condition is determined by the uniform shaping of the filler elements. Therefore, a manufacturing method and also a device for carrying out this method are required so that the changes occurring in the expanded metal, when it is converted into filler elements, take place uniformly and in a defined manner, and consequently the filler elements which are produced not only exhibit the same external shape and dimensions, but also they possess approximately the same defined internal structure.
If, for example, one were merely to cut rectangular sections from the two-dimensional lattice-structure of the expanded metal and then crush these in a random manner until they assumed an approximately spherical outer shape, the following situation would always arise: within the spherical outer contour, the material would be highly compressed at certain points, while at other points large cavities would remain. This would result in uneven heat transmission and would thus reduce the protective function. It has been found that filler elements having a spherical shape approx. 2 cm in diameter are suitable for subsequently filling automobile fuel tanks and small gasoline containers.
For the manufacture of these filler elements of expanded metal, procedures are known wherein at least in the final step, the ultimate shape of the filler element is generated by compressing the lattice work into a spherical shape between two halves of a mold which together form the desired spherical mold cavity. One of these mould sections might also be equipped with an ejector to push out the finished filler element. In order to achieve a uniform and defined distribution of the lattice work within the spherical shape of the finished filler element, however, it is necessary in particular to carry out certain processing steps ahead of the final shaping step.